Sniper and Trunk Battery help

"Working on 69 Dart big block project with my son and have run into some electrical difficulties with the EFI and electrical upgrade. ANY help and opinions would be greatly appreciated. Using the wiring diagram below supplied by "Crackedback" in a previous post I read.

Battery in trunk. I have a Painless Performance High Amp Alt. Shutdown relay that I would like to wire in the system.
Single wire Mopar 100+ amp alternator

Need to wire into disconnect switch BUT the diagram has the feed wire going to the non battery side of the switch.
The Painless relay instructions specifically state to wire the feed to the battery side and has an 18 gauge wire that is supposed to mount on the other side of the switch would surely be fried when the switch is closed ?

THAT means all the feed goes through starter solenoid SO,

I believe I also need a continuous duty starter solenoid that will also support EFI correct? The old style had no diode which could fry my system? Any recommendations on a part?

I have also already bought the wrong disconnect switch as the second pole not rated amperage wise for the alternator output for this application so I could use a recommendation on that as well.

Anybody willing to tell me how you accomplished this or have recommendations?


Thanks
Brian